Channels ▼

Eric Bruno

Dr. Dobb's Bloggers

Interesting Java Puzzler

June 11, 2009

Here's an interesting code puzzler I found on Alex Miller's technical blog:

<font color="#7f0055">import</font> java.util.HashMap;  
<font color="#7f0055">import</font> java.util.HashSet;  
<font color="#7f0055">import</font> java.util.Map;  
<font color="#7f0055">import</font> java.util.Set;  
<font color="#7f0055">import</font> java.util.concurrent.ConcurrentHashMap;  
  
<font color="#7f0055">public class</font> EntrySetSize {  
  
  <font color="#7f0055">public static void</font> main(String[] args) {  
    printSetSize(<font color="#7f0055">new</font> ConcurrentHashMap());  
    printSetSize(<font color="#7f0055">new</font> HashMap());  
  }  
  
  <font color="#7f0055">private static void</font> printSetSize(Map map) {  
    map.put("<font color="#2a00ff">hello</font>", "<font color="#2a00ff">world</font>");  
    map.put("<font color="#2a00ff">world</font>", "<font color="#2a00ff">hello</font>");  
    Set set = <font color="#7f0055">new</font> HashSet(map.entrySet());  
    System.out.print(set.size() + " ");  
  }  
}  

 The puzzle is to figure out what sequence of numbers this code will print when executed. Is it:

a) 2  2

b) 1  2

c) 0  2

d) something else

To find the answer (hint: it varies on different versions of the JDK) check out Alex's  blog here.

 He also has an excellent description of the puzzler's behavior.

-EJB 

Related Reading


More Insights






Currently we allow the following HTML tags in comments:

Single tags

These tags can be used alone and don't need an ending tag.

<br> Defines a single line break

<hr> Defines a horizontal line

Matching tags

These require an ending tag - e.g. <i>italic text</i>

<a> Defines an anchor

<b> Defines bold text

<big> Defines big text

<blockquote> Defines a long quotation

<caption> Defines a table caption

<cite> Defines a citation

<code> Defines computer code text

<em> Defines emphasized text

<fieldset> Defines a border around elements in a form

<h1> This is heading 1

<h2> This is heading 2

<h3> This is heading 3

<h4> This is heading 4

<h5> This is heading 5

<h6> This is heading 6

<i> Defines italic text

<p> Defines a paragraph

<pre> Defines preformatted text

<q> Defines a short quotation

<samp> Defines sample computer code text

<small> Defines small text

<span> Defines a section in a document

<s> Defines strikethrough text

<strike> Defines strikethrough text

<strong> Defines strong text

<sub> Defines subscripted text

<sup> Defines superscripted text

<u> Defines underlined text

Dr. Dobb's encourages readers to engage in spirited, healthy debate, including taking us to task. However, Dr. Dobb's moderates all comments posted to our site, and reserves the right to modify or remove any content that it determines to be derogatory, offensive, inflammatory, vulgar, irrelevant/off-topic, racist or obvious marketing or spam. Dr. Dobb's further reserves the right to disable the profile of any commenter participating in said activities.

 
Disqus Tips To upload an avatar photo, first complete your Disqus profile. | View the list of supported HTML tags you can use to style comments. | Please read our commenting policy.
 


Video